Composition for preventing deposition and corrosion in oil well equipment



l atenied Nov. 3, 1953 UNITED STATES TENT OFFICE TION' AND CORROSION. IN

EQUIPMENT H1 WELL Clark D. Core, Seguin, and Edward N. Jones,

Pettus,

'1ex.;v said Core assignor to Texas Acidizers, Incorporated, Seguin,Tex., a. corporation or Texas Nollrawing- Application July 19, 1950,.Serial.No. 174,788"

This invention relates to compositions for use in increasing theefiiciency and productivity of oil, gas or water producing wells.

The primary object of this invention is tov provide compositions whichare more efiective in simultaneously preventing corrosion and scaledeposition on the metal surface of well equipment, such as casing,tubing, surface connections, flow lines, separators, heaters and tanksthan the conventional products presently employed.

Most fluids that come out of earth formations contain many complexinorganic as well as. organic chemicals which include compounds ofcalcium, magnesium, potassium, sodium, iron, carbon, hydrogen, bariumand sulphur. While, the compounds are trapped in the earth formation,they existv in the fluids in a. state of. equilibrium which can bedisturbed by changes. of heat and pressure. When the well is produced,the fluids leave the relatively high temperature and pressure conditionsfound at the formation and ascend toward the. surface of the earth whilethe temperature and pressure decrease. librium. so upset causes theformation of new compounds, such as carbonic. acid. and acetic acid,which have a marked corrosive eifect on steel, and also causes theformation of compounds which precipitate ont. upon the steel as. a hardscale deposit. Calcium carbonate, calcium sulphate, magnesium sulphateand iron sulphidev are several. of the compounds which precipitate. outas scale. The deposition of. the scale compounds and the corrosivecompounds remains on the metallic equipment until holes form therein,making immediate replacement necessary. This not only interrupts theproductio in the well, but also requires costly replacements,particularly in the case of high pressure wells Where even one smallhole can start a series of costly consequences. Therefore, there is aconstant demand in this art for compositions which will simultaneouslyprevent corrosion and also prevent the depositions of hard scale on thewell equipment. The present composition effectively performs this dualfunction in a manner not heretofore possible. with the; manycompositions presently available onthe market.

One. of the important ingredients in thepresent. composition is. awater-soluble, alkali metal arsenite, such assodium or potassiumarsenite.

As. stated hereinabove, it is not. only necessary to provide a corrosioninhibitor which will effectively cover the metallic well equipment, butalso an ingredient which will remove existing scale Claims; (0].252-855)- The equiand prevent further scale deposition inasmuch as thedestruction of well equipment is due to a combination of" both thecorrosion of the equipment by the acids in the well fluids and the scaledepositiononthe equipment. Accordingly, the present composition includesa Water-soluble, a1-

kali metal hexametaphosphate, such as sodiumorpotassiumhexametaphosphate, which accomplishes this purpose by holding insolution inprcper chemical equilibrium the compounds that wouldotherwise precipitate to form the scale. The sodium hexametaphosphateforms soluble complex compounds-- with the scale-forming compoundsalready in solution; the complex compounds being carried harmlessly' outof the Well equipment in solution with the fluids being produced.

It is well known in this artthat crude oil or.

paraffin films form upon the surfaces ofthe;

metal equipment which act as insulation between the metal surface andthe treating solutions, and that this is further aggravated by thepresence of resistant emulsions. of the water-oil and oilwater type.Accordingly, an. effective composition for preventing. deposition ofscalev and corrosion must alsoinclude an ingredient. whichwilleffectively remove the crude oil. or parafiin film from the metalsurfaces and. at the same time effectively break up the resistantemulsions. Experimentation has been conducted with a number ofdetergents or Wetting agent'sfor incorporationv with the arsenite andhexametaphosphate, but it. hasv been found. that only a few of thesewetting agents are really effective for the dual purpose. of removingthe crude oil or paraffin film and the breaking up of the resistantwater-oil and. oil-Water emulsions. Certain of the Wellknown Aerosolcompounds have been employed to. advantage. Aerosol OS, has been foundto have the best. properties, while it has also been found that AerosolMA, Aerosol AY and Aerosol 15 could also be employed in the composition.Aerosol OS is a water soluble wetting agent or detergent otherwiseknown. as. isopropyl naphthalene sodium sulfonate, Aerosol MA is dihexylsodiumsulfosuccinate, Aerosol AY is diamyl sodium sulfosuccinate; andAerosol IB is diisobutyl sodium sulfosuccinate;

It will thus be seenthat" the basic compositionherein providedforpreventing deposition of scalewater-oil emulsions- This compositionmay be a dry or solid composition or may be an aqueous solutiondepending upon the-manner of applicaproportions of the ingredientsemployed:

EXAMPLE I a Per cent by weight Sodium arsenite, 40% aqueous solution byweight "14.0-45.0

Sodium hexametaphosphate 4;0-45.0 Aerosol O I 0.4 Remainder-Water.

- As the corrosion and scale deposition problems vary greatly indifferent areas,chemical analysis of the well fluidsshould be made todetermine starch and mold the mixture, after which the tion. Theexamples which follow illustrate the water isexpelled by heatevaporation.

, Thus, it will be seen that novel compositions 'are'provided which, dueto their power to re- -move as well as prevent the formation of scaledepositions in well tubing, surface connections and flow lines, free andunobstructed flow of the well fluids is obtained throughoutsubstantially the entireproductive life of the Well. Inasmuch as thesecompositions also contain surface-active materials which not only'removecrude oiland paraffin deposits on the metallic equipment, but

the variations which must-be made in the pro portions of the aboveingredients, In the case of highlycorrosive wells in which very littlescale develops, it would be necesary to increase the arseniteconcentration and decrease the phosphate concentration correspondingly.On the other hand, if a well has extreme scale develop-.

ment and very little corrosion, the phosphate concentration should beincreased and the arsenite concentration correspondingly decreased.

Inasmuch as aldehydes, such as formaldehyde, act as corrosion inhibitorsin metallic oil well equipment, and particularly because of a reactionbetween formaldehyde and hydrogen sulphide in 1 the well fluid toproduce a protective film, formaldehyde may be added to the abovecomposition to replace some of the water and the preferred percentage byweight of the added formaldehyde The preferred composition and one whichhas proven highly efiective in widespread areas is given in thefollowing example: 1

EXAMPLE II Per cent by weight Sodium arsenite, 40% by weight of anaqueous solution 45.0 Sodium hexametaphosphate 4.0 Aerosol OS 0.4

Remainder-Water.

It will be understood that the above compositions can be administered anumber of different ways, but preferably will be injected into theannular space between the well tubing and the long string of casing.-The composition trickles down the metallic surfaces of the wellequipment to the bottom of the tubing and is picked up in smallquantities, but continuously,

by the well fluids ascending inside of the tubing. Instead of theaqueous solutions mentioned hereinabove, a solid mixture of theingredients, either in stick or pellet form, may be administered in theoil well, and the following example gives the ingredients in theirproper percentage by weight for the solid composition:

EXAMPLE III Per cent Sodium arsenite powder 24-71 Sodiumhexametaphosphate powder 24-71 Aerosol OS powder 2 Starch 3 The starchis used as a binder and a small amount of water is used initially todissolve the sodium sulfonate to act as a also act as demulsificationagents for effectively breaking up the oil-water and water-oilemulsionsnormally found in wells, both the corrosion inhibitingarsenites and the scale preventing hexametaphosphates can at all timesperform their desired functions efiectively.

, While preferred embodiments of the present I composition have beendescribed hereinabove, it will. be understood that minor variations inthe composition can be made by those skilled in'the I art withoutdeparting from the spirit of the invention or the scope of the appendedclaims.

Having described the invention, what is claimed as new is:

11A composition for removing and preventing scale deposition andpreventing corrosion in oil well'equipment comprising 4-45% by weight ofI a 40% aqueous solution of an alkali metal arsenite, 4-45% by weight ofan alkali metal hexametaphosphate and a minor amount of surfaceactivedemulsification agent, the balance being water. a

2.'The composition of claim 1 wherein said demulsification agent isselected from the class consisting of isopropyl naphthalene sodium sul-.

fonate, dihexyl 'sodium sulfosuccinate, diamyl sodium sulfosuccinate anddiisobutyl sodium sulfosuccinate.

3. The composition of claim 1 wherein said arsenite is sodium arseniteand said hexametaphosphate is sodium hexametaphosphate.

4. A composition for removing and preventing scale deposition andpreventing corrosion in oil References Cited in the file Of this patentUNITED STATES PATENTS Number Name Date 935,695 Schultze Oct. 5, 19091,877,504 Grebe et a1 Sept. 13, 1932 1,903,041 Hall et al. Mar. 28, 19332,204,580 De Groote June 18, 1940 2,262,737 De Groote Nov. 11, 19412,426,318 Menaul Aug. 26, 1947 2,429,594 Case Oct. 28, 1947 2,468,163Blair et al. Apr. 26, 1949

1. A COMPOSITION FOR REMOVING AND PREVENTING SCALE DEPOSITION ANDPREVENTING CORROSION IN OIL WELL EQUIPMENT COMPRISING 4-45% BY WEIGHT OFA 40% AQUEOUS SOLUTION OF AN ALKALI METAL ARSENITE, 4-45% BY WEIGHT OFAN ALKALI METAL HEXAMETAPHOSPHATE AND A MINOR AMOUNT OF SURFACEACTIVEDEMULSIFICATION AGENT, THE BALANCE BEING WATER.